The Powerglide transmission was one of the first automatic transmissions developed by General Motors, initially introduced in 1952. Although General Motors itself phased out the Powerglide transmission in 1973, the basic design of the aluminum housing Powerglide, introduced in 1962, is still used today, especially in niche automotive applications, including in automobile powertrains designed for racing. The Powerglide transmission design has remained popular for drag racing due, in part, to the strength, durability and simplicity of the two-speed design. Indicative of the Powerglide's continued popularity, it is today possible to purchase a newly manufactured complete Powerglide transmission or to build an entire Powerglide transmission from aftermarket parts, and a cottage industry has developed around improving the performance of the Powerglide transmission design in racing applications. Because of this history, entire transmissions as well as complete replacement parts built to original equipment (“OE”) dimensions and specifications continue to be readily available in the market. Thus, for the sake of clarity, “OE Powerglide” as used herein refers specifically to Powerglide transmissions as originally manufactured by General Motors, while Powerglide, generally, includes both OE Powerglide transmissions and all transmissions based on the OE Powerglide design, but which may have aftermarket modifications. FIG. illustrates, in cross-section, the parts of an OE “aluminum case” Powerglide transmission. Table 1, at the end of the specification, includes a list of the parts shown in FIG. 6, which is extracted from a Powerglide service guide, circa 1965 (available for download at http://cogpro.com/chapters/F-Powerglide/index.htm), which is incorporated by reference herein in its entirety.
As an early automatic transmission design, the Powerglide differs from current designs in some respects. Most rotating parts in modern automotive transmissions have predefined, finite limitations on axial movement (commonly controlled with thrust washers/bearings) and radial movement (commonly controlled with bushings or roller bearings). These constraints help to stabilize the components and control excessive vibration. The ring gear of the Powerglide transmission, however, has no supports specifically intended to limit radial movement. The ring gear does have contact surfaces to limit axial movement to some extent, however, still the total axial movement can be excessive in many situations.
In applications with high horsepower, such as drag racing, it can be particularly important to stabilize the rotating parts of the transmission to reduce the axial and radial movement to prevent wear. With the Powerglide transmission, the combination of the radial and axial movements can lead to uncontrolled movement of the ring gear off of the transmission centerline and can also cause undesirable vibrations, particularly at higher rotational speeds, such as those seen in racing transmissions.
Within the Powerglide transmission, the ring gear engages pinion gears of a planet carrier and also has a splined, rearwardly directed section that engages the reverse clutch friction plates. The portion of the ring gear engaging the reverse clutch friction plates is not well supported. While operating in forward gear ranges, the reverse clutch is not engaged and, as a result, the reverse clutch friction plates follow the oscillations of the ring gear. The oscillations and misalignment of the ring gear affects ring gear and planet carrier wear, ring gear reverse clutch spline wear, and fatigue of the reverse clutch friction plates. For example, the thin steel spline of the reverse clutch friction plates wear and deform from the pulsing that occurs, pulsing causes additional wear on the ring gear spline where cavities form as a result and the friction plates may even fracture. These deformities can lead to capturing of the friction plates, further restricting the free movement of the friction plates being driven by the ring gear oscillations. Furthermore, the misalignment of gear teeth can result in uneven and premature wear of gear teeth. The oscillations of the ring gear cause greater friction in the transmission which results in less overall horsepower.